Figure 5. . Efficiency of linking reactions.

Reactions in solution rely upon diluted reactants coming into contact in order to react (A), whereas in the solid phase the reactants can be concentrated together to aid in coupling efficiency (B). If, however, the reactants cannot penetrate the solid structure completely, an inhomogeneous reaction can occur which can lead to radiopaque groups more prevalent at the surface of the beads and a halo-like image observed by micro-CT (C & D).

CT: Computed tomography.